1. Field of the Invention
Although the United States attempts to control pests such as weeds, insects, nematodes, and fungi with about 2 billion pounds of pesticides per year, these pests are still responsible for annual farm production losses of 35 billion dollars. This loss is equivalent to 30% of the total market value of farm products. Part of the problem involves a lack of full availability of the pesticide to the target as a result of wind, evaporation, leaching, degradation, and waste on nontargeted areas. One way of achieving more efficient pesticide usage is through controlled release formations capable of reducing rates of application, allowing fewer applications, limiting control to targeted areas, reducing evaporative and degradative losses, and providing a slow release of pesticide concurrent with the presence of moisture and soil microorganisms. In addition, controlled release provides for a safer environment, reduces toxicity to desirable plants, makes pesticides safer to handle, and extends residual life of pesticides without carryover into the subsequent growing season.
This invention relates to a novel method of encapsulating pesticides and other chemical biological agents for controlling their release and to the compositions prepared thereby.
2. Description of the Prior Art
Various approaches to the controlled release of chemical biological agents by means of a starch-based encapsulating material have previously been disclosed. In U.S. Pat. Nos. 4,277,364 and 4,344,857 Shasha et al. disclose methods of encapsulation whereby a polyhydroxy polymer xanthate and a coupling agent are reacted from a single phase to form an insolubilized xanthide matrix, thereby entrapping the active agent. The Shasha et al. system has the advantage of operating in both aqueous and nonaqueous two-phase systems, as well as in single-phase systems in which the matrix-forming materials and the core material are soluble in the same solvent. Another advantage is that the entire reaction mixture is converted into a solidified mass which is readily dried and ground into a usable product after pressing out excess water. This obviates the recovery from a liquid medium as necessitated by most coacervation and interfacial polymerization methods. However, widespread commercial acceptance of the Shasha et al. methods has been hindered by the reluctance of the industry to handle carbon disulfide which is both flammable and toxic.
In U.S. patent application Ser. No. 202,396, filed Oct. 30, 1980, now U.S. Pat. No. 4,382,813, Shasha discloses a system for encapsulating certain types of pesticidal agents by the rapid insolubilization of a starch-containing material alkoxide with a bivalent cation selected from the group of calcium, barium, and strontium. While this system is applicable to water-insoluble agents, it is not particularly suitable for those which are water-soluble, nor for substances susceptible to alkali degradation.